1. Field of the Invention
The present invention relates to audio headsets, and, more particularly, to audio headsets that may be used within an aircraft during flight.
2. Description of the Related Art
Traditionally, wired headsets are used within aircrafts by pilots, passengers, and others inside the plane. Currently, the Federal Aviation Admission does not allow wireless communications that can interfere with avionics during flight. Avionics are susceptible to interference from known short range wireless communications devices, such as cell phones, Bluetooth headsets, and other transmitting Personal Data Assistant devices. This limits the technology options available for headsets that are used inside the aircraft. The transmission systems used in the prior art are based on single carrier-based transmissions. In these systems, the majority of the transmission energy is concentrated around the carrier frequency, such as 2.4 GHz or 900 MH, for example. Typically, the short range wireless transmissions of the prior art use 0.75 to 1.0 watt of power in these narrow frequency bands. These high power, narrow frequency band transmissions can adversely affect the avionics, especially since the avionics are not designed to be immune to such high power transmissions.
Prior art, Bluetooth and related technologies use narrow band carriers, and they use limited frequency-hopping (2.400 GHz-2.480 GHz). FIGS. 1a and 1b illustrate an exemplary narrow band carrier in the time domain and frequency domain, respectively. Direct sequence spread spectrum (DSSS) and frequency-hopping spread spectrum (FHSS) methods typically occupy larger bandwidths than a simple narrow band transmission. These technologies do improve communication bandwidth and resistance to jamming due to the slightly larger bandwidth However, even with the complex FHSS techniques, these transmissions are susceptible to interference. The bandwidth improvements are in the range of only a few MHz. For example, if an industrial, scientific and medical (ISM) band jammer is effective in the frequency range of 2.40-2.48 GHz, then a Bluetooth device could not function in that environment.
The transmission systems used in the prior art are mostly narrow band carrier-based, and have limited allocated bandwidths to transmit signals. The limited channel capacity results in poor audio quality/intelligibility and unreliability. Channel capacity in a communication channel is given by the Shannon-Hartley theorem, which states that the amount of information delivered via radio is logarithmically proportional to signal strength expressed as signal-to-noise ratio, and directly proportional to the bandwidth. Since the bandwidth in these narrow band channels is limited, the channel capacity is also limited. Due to this limited availability of bandwidth, these systems have limited channel capacity, and these systems fail to implement the necessary error corrections or repeated packet transmissions needed for critical communications.
In the case of poor communication links, the packet errors in these systems will affect the audio quality and intelligibility of the communications. In some situations, the aircraft headset provides mission critical communications between the pilot and the ground tower. Therefore, packet errors in the transmissions and poor intelligibility are not acceptable for this application.
What is needed in the art is a wireless headset that is suitable for use in aircraft and that avoids the above-mentioned problems and disadvantages.